1. Field of the Invention
The present invention relates to a toner manufacturing method.
2. Description of the Related Art
In an electrophotographic image forming apparatus, a surface of an image bearing member is charged uniformly by a charging section (charging step), the surface of the image bearing member is exposed by an exposure section, and charges on the exposed surface are dissipated, thereby forming an electrostatic latent image on the surface of the image bearing member (exposure step). Then, a toner which is fine colored powder having charges is adhered to the electrostatic latent image to make a visible image (developing step), and the obtained visible image is transferred onto a recording medium such as paper (transfer step). Further, the visible image is fixed onto the recording medium by a fixing section under application of heat and pressure or with other fixing method (fixing step). Through these steps, an image is formed on the recording medium. Moreover, cleaning of the image bearing member is performed for removing the toner which has not been transferred onto the recording medium and thus remains on the surface of the image bearing member (cleaning step).
In recent years, with trend of improvement in image quality of a full-color image, in order to enhance accuracy of color reproduction by color mixing, an intermediate transfer system in which images of respective colors are sequentially formed on one transfer member while being overlaid on top of one another and the formed full-color images are collectively transferred onto a transfer medium is employed as a transfer method.
Moreover, examples of a method for fixing a toner include a heating fixing method in which a toner is fixed onto a recording medium by melting the toner under application of heat and a pressure fixing method in which a toner is fixed on a recording medium by plastically deforming the toner under application of pressure.
The toner used for such image formation needs to have functions required not only in the developing step but also in each of the transfer step, the fixing step and the cleaning step. For example, the developing step requires sufficient durability against stress caused by stirring in a developer tank and the like, and the transfer step requires high transfer property from a transfer member to a recording medium. In addition, the fixing step requires low-temperature fixation property in terms of energy saving.
In order to realize low-temperature fixation property, molecular weight of a binder resin constituting toner particles is reduced, or a release agent is added to toner particles to reduce a softening temperature of the toner particles. At the same time, it is necessary to prevent occurrence of offset that the composition of the toner remaining on a fixing member is fixed onto a recording medium to contaminate an image.
Meanwhile, in order to enhance transfer property of the toner, for example, the toner is spheroidized, or a spacer is applied to the surface of the toner by adding fine particles whose particle size is around one-tenth to one-thirtieth the particle size of the toner, to the toner.
However, transfer property is enhanced by spheroidizing the toner, but a problem is caused that the toner slips through a blade and contaminates a transfer member to cause a defective image. In addition, fine particles having the size used as a spacer are separated from the toner surface to cause problems such as contamination of the interior of a developer tank or a drum, and a white spot.
In order to solve such problems, Japanese Unexamined Patent Publication JP-A 5-331215 (1993) discloses a spherical toner having a projection formed on the surface of dispersion-polymerized particles to have irregularity on the particle surface. In addition, JP-A 8-171230 (1996) discloses a toner manufacturing method in which at least one kind of fine powder selected from among a chromatic colorant, a flowability improver, an abrasive agent, an electric charge controlling agent, a magnetic substance and inorganic fine particles is adhered to the particle surface of binder resin powder and mechanical impact is allowed to act to keep the fine powder on the particle surface of the binder resin powder by implantation.
However, in the toner disclosed in JP-A 5-331215, a second monomer is polymerized in the dispersion-polymerized particles of a first monomer to thereby form a projection, but a lot of minute projections are formed and it is difficult to form a projection having the size larger than one-twentieth the particle size of toner. Such a toner shows cleaning property enhancing effect to a certain degree by minute projections compared to the spherical toner obtained by a dispersion polymerization method, but does not show sufficient enhancing effect for other toner properties.
Further, in the toner disclosed in JP-A 8-171230, although the fine powder is implanted and kept on the particle surface of the binder resin powder by mechanical impact, the fine powder and the binder resin particles are not attached to each other by fusion, so that the fine powder is easily separated from the toner surface, causing image defects. In addition, by keeping not-hot melt fine powder on the toner surface, hot melting property of toner base particles containing the binder resin powder is affected and a release agent component is inhibited from bleeding out, resulting in lowering in fixation property of the toner.